How to add backports to /etc/apt/sources.list

Question

I've read that some of the necessary pipewire modules for bullseye are available through the backports repo. I tried this, but had problems as described below:

Add following line to /etc/apt/sources.list :

deb http://deb.debian.org/debian bullseye-backports main contrib non-free
then run:
sudo apt update
Get:1 http://deb.debian.org/debian bullseye-backports InRelease [49.0 kB]
Hit:2 http://archive.raspberrypi.org/debian bullseye InRelease
Err:1 http://deb.debian.org/debian bullseye-backports InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E98404D386FA1D9 NO_PUBKEY 6ED0E7B82643E131
Hit:3 http://raspbian.raspberrypi.org/raspbian bullseye InRelease
Reading package lists... Done
W: GPG error: http://deb.debian.org/debian bullseye-backports InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E98404D386FA1D9 NO_PUBKEY 6ED0E7B82643E131
E: The repository 'http://deb.debian.org/debian bullseye-backports InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

What's going on here? Can anyone help?

Answer 1

NOTE : Please note that as per the QUESTION, this answer applies to the 'bullseye' distribution - not 'bookworm'.

I think I've resolved this - thanks to @goldilocks' Comment. For anyone else suffering from the "Raspberry Rash", here's what to do:

1. Note first that the URL indicates this is a Debian repo - NOT a raspberrypi URL. Thus, the need for a different GPG key! (silly me)

2. Therefore, we must get and install the Debian GPG key; accomplished as follows:

# download the Debian key:
$ curl -O http://http.us.debian.org/debian/pool/main/d/debian-archive-keyring/debian-archive-keyring_2023.4_all.deb
install the Debian key:
$ sudo dpkg -i debian-archive-keyring_2023.4_all.deb
Selecting previously unselected package debian-archive-keyring.
(Reading database ... 114968 files and directories currently installed.)
Preparing to unpack debian-archive-keyring_2023.4_all.deb ...
Unpacking debian-archive-keyring (2023.4) ...
Setting up debian-archive-keyring (2023.4) ... 

3. And you can now update & install the pipewire upgrade from bullseye-backports:

$ sudo apt update
...
$ sudo apt install -t bullseye-backports pipewire pipewire-audio-client-libraries
...

NOTE: Don't forget to add the following line to /etc/apt/sources.list :

deb http://deb.debian.org/debian bullseye-backports main contrib non-free

And there's more:

Other packages are available; here's how to see them:

aptitude -t bullseye-backports search '~U~Abullseye-backports' 

_{You may need to install aptitude first!}

And here's the Debian backport documentation.

Cautionary Notes:

Before adding any of the Debian backports to your system, there are some things you should know:

A. Know first that you should have a good backup before installing any Debian backport.

B. Despite statements on Debian's website, not all Debian backports are compatible with all Raspberry Pi models.

The "bottom line" is this:

bullseye-backports should not be used unless you're on a Raspberry Pi 3 or later model hardware - or a Zero 2W.

C. You should know how to "revert" packages installed from backports. For example, if you just used Debian's bullseye-backports to install a later version of pipewire on your Raspbian system as follows:

sudo apt install -t bullseye-backports pipewire pipewire-audio-client-libraries

You can "revert" that installation from bullseye-backports back to bullseye as follows:

sudo apt install pipewire/bullseye pipewire-audio-client-libraries/bullseye

Epilogue:

As it turns out, parts of this answer were already provided by John Goerzen in his blog post "Installing Debian Backports on Raspberry Pi". This is a very interesting read. Note in particular his recommendations to use the form apt-get -t bullseye-backports install. And I share his annoyance with the RaspberryPi organization. REF my latest row re their documentation. Perhaps fortunately (remains to be seen) the "worker bees" at RPiOrg don't share the same attitude as the owner's wife!